Axle stabilizers, for which the drive unit of this type is designed, are used, in general, to reduce or even fully compensate rolling movements of the body around the longitudinal axis of the vehicle, which occur because of the lateral acceleration during travel in curves. The wheel carriers, which usually belong to the same axle of the vehicle, are connected with one another via a split axle stabilizer bar, and the axle stabilizer parts are fixed at the same time rotatably at the vehicle body by means of separate bearing elements. The ends of the stabilizer halves, which are located opposite each other and are not fixed to the wheel carrier, are coupled by means of an intercalated rotary drive. The drive unit arranged between the two stabilizer halves as a part of the rotary drive is used to twist the axle stabilizer ends in relation to one another, which may markedly increase the stability of the vehicle against rolling.
When such hydraulic drive units are used, it shall be guaranteed for safety reasons that no uncontrolled adjustment of the rotary drive and consequently no unintended change in the properties of the axle stabilizer are brought about in case of failure of the corresponding hydraulic circuit or in case of errors in the electrical system of the motor vehicle. The hydraulic drive units known from the state of the art are equipped for this purpose with expensive and bulky pressure reservoirs with valve systems belonging to them.
Moreover, automatic adjustment of the rotary drive into a predefined neutral position, in which the axle stabilizer assembly unit has a medium torsional rigidity, is desirable in case of the above-described failures of the hydraulic and electrical systems of the motor vehicle.